Hormone  

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Kunstformen der Natur (1904) by Ernst Haeckel
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Kunstformen der Natur (1904) by Ernst Haeckel

A hormone (from Greek ὁρμή, "impetus") is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one cell to another. All multicellular organisms produce hormones; plant hormones are also called phytohormones. Hormones in animals are often transported in the blood. Cells respond to a hormone when they express a specific receptor for that hormone. The hormone binds to the receptor protein, resulting in the activation of a signal transduction mechanism that ultimately leads to cell type-specific responses.

Endocrine hormone molecules are secreted (released) directly into the bloodstream, whereas exocrine hormones (or ectohormones) are secreted directly into a duct, and, from the duct, they flow either into the bloodstream or from cell to cell by diffusion in a process known as paracrine signalling.

Recently it has been found that a variety of exogenous modern chemical compounds have hormone-like effects on both humans and wildlife. Their interference with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body can change the homeostasis, reproduction, development, and/or behavior, just as endogenously produced hormones do.

Important human hormones

See: List of human hormones

See also




Unless indicated otherwise, the text in this article is either based on Wikipedia article "Hormone" or another language Wikipedia page thereof used under the terms of the GNU Free Documentation License; or on original research by Jahsonic and friends. See Art and Popular Culture's copyright notice.

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